<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <script>

        function myForEach(arr , f) {
            for(var i = 0 ; i < arr.length ; i++) {
                // 你想干的事情
                // console.log(arr[i]) ;
                // document.write(arr[i]) ;
                f(arr[i]);
            }
        }


        myForEach([1,2,3,4] , function(v) {
            console.log(v);
        });


        // 数组求和
        var sum = 0 ;
        myForEach([1,2,3,4] , function(v) {
            sum += v ;
        })
        console.log(sum);
 

    </script>
    
</body>
</html>